1. Field of the Invention
The present invention relates to an optical disk reproducing method and apparatus.
2. Related Background Art
Recently, an effort has been made to develop an optical recording/reproducing method which meets various demands such as a high density, a large capacity, a high access speed, or a high recording/reproducing speed, and a recording/reproducing apparatus and a recording medium (disk) used for this method.
Information is recorded by, e.g., utilizing three-dimensional patterns formed on a substrate or reflectance difference caused due to a phase change between crystal and amorphous phases, or by forming a recording layer consisting of a magnetic film on a substrate to record information by difference in direction of magnetization, thereby forming a recording mark.
A laser beam is generally used to reproduce the recording marks. The laser beam is formed to be a spot as small as the diffraction limit defined by the wavelength of the laser beam to read the phase shape of the disk, the reflectance difference, rotation of the polarized light caused due to the magnetooptical effect of the magnetic film or the like. Because of the noise of the apparatus, a better S/N ratio can be obtained by increasing the reproduction light amount. On the other hand, in a rewritable optical disk, information is recorded by heat using optical energy. Therefore, when the information on the medium is to be reproduced, the power must be controlled not to destroy the information by the reproduction beam.
In recent years, an information recording method which changes the recording frequency in accordance with the radial position on the disk to realize higher-density recording has been proposed. However, when the recording frequency is changed in accordance with the radial position on the disk, the recording frequency at the outer peripheral portion is increased to broaden the reproduction frequency band at the outer peripheral portion. For this reason, the S/N ratio at the outer peripheral portion is degraded as compared to that at the inner portion.
In another information reproducing method, a multilayered structure of magnetic layers is formed to utilize magnetic super resolution due to heat of the reproduction beam, thereby reading high-density-recorded marks (MORIS' 91, 18-I-06). However, in the above method, the medium temperature at the reproduction position must be within a predetermined range. Even in one disk, the temperature is increased by the reproduction beam in a different way depending on the rotational speed or linear velocity. Therefore, the above method can be hardly realized.
An object of the present invention is to solve the above problems posed in the conventional optical disk reproducing apparatus.
As a result of extensive studies of the present inventor, a novel optical disk reproducing method and apparatus have been invented.
According to the first aspect of the present invention, there is provided an optical disk reproducing method using an optical disk reproducing apparatus comprising an optical disk, optical disk rotating means, a light source for irradiating a reproduction beam on the optical disk, light condensing means for condensing the reproduction beam on the optical disk, detection means for detecting a beam passing through or reflected by the optical disk, and position detection means for detecting a reproduction beam condensing position in a radial direction on the optical disk, wherein an intensity of the reproduction beam is changed in accordance with the reproduction beam condensing position on the optical disk.
According to the second aspect of the present invention, there is provided an optical disk reproducing method using an optical disk reproducing apparatus comprising an optical disk, optical disk rotating means, a light source for irradiating a reproduction beam on the optical disk, light condensing means for condensing the reproduction beam on the optical disk, detection means for detecting a beam passing through or reflected by the optical disk, and position detection means for detecting a reproduction beam condensing position in a radial direction on the optical disk, wherein an intensity of the reproduction. beam in reproduction of an outer region of the disk is set to be larger than that in reproduction of an inner region of the optical disk.
According to the third aspect of the present invention, there is provided an optical disk reproducing method using an optical disk reproducing apparatus comprising an optical disk, optical disk rotating means, a light source for irradiating a reproduction beam on the optical disk, light condensing means for condensing the reproduction beam on the optical disk, detection means for detecting a beam passing through or reflected by the optical disk, and position detection means for detecting a reproduction beam condensing position in a radial direction on the optical disk, wherein an intensity of the reproduction beam is changed in accordance with a linear velocity of the optical disk at the reproduction beam condensing position.
According to the fourth aspect of the present invention, there is provided an optical disk reproducing apparatus comprising an optical disk, optical disk rotating means, a light source for irradiating a reproduction beam on the optical disk, light condensing means for condensing the reproduction beam on the optical disk, detection means for detecting a beam passing through or reflected by the optical disk, position detection means for detecting a reproduction beam condensing position in a radial direction on the optical disk, and reproduction beam drive means for changing an intensity of the reproduction beam in accordance with the reproduction beam condensing position.
According to the fifth aspect of the present invention, there is provided an optical disk reproducing apparatus comprising an optical disk, optical disk rotating means, a light source for irradiating a reproduction beam on the optical disk, light condensing means for condensing the reproduction beam on the optical disk, detection means for detecting a beam passing through or reflected by the optical disk, position detection means for detecting a reproduction beam condensing position in a radial direction on the optical disk, and reproduction beam drive means for changing an intensity of the reproduction beam in accordance with a linear velocity of the optical disk at the reproduction beam condensing position.
According to the sixth aspect of the present invention, there is provided an optical disk reproducing method using an optical disk reproducing apparatus comprising an optical disk, optical disk rotating means, a light source for irradiating a reproduction beam on the optical disk, light condensing means for condensing the reproduction beam on the optical disk, detection means for detecting a beam passing through or reflected by the optical disk, and position detection means for detecting a reproduction beam condensing position in a radial direction on the optical disk, wherein an intensity of the reproduction beam is changed in accordance with a linear velocity of the optical disk at the reproduction beam condensing position so that a substantially constant medium temperature is obtained at a reproduction beam irradiation portion of the optical disk.
According to the seventh aspect of the present invention, there is provided an optical disk reproducing apparatus comprising an optical disk, optical disk rotating means, a light source for irradiating a reproduction beam on the optical disk, light condensing means for condensing the reproduction beam on the optical disk, detection means for detecting a beam passing through or reflected by the optical disk, position detection means for detecting a reproduction beam condensing position in a radial direction on the optical disk, and reproduction beam drive means for changing an intensity of the reproduction beam in accordance with a linear velocity of the optical disk at the reproduction beam condensing position so that a substantially constant medium temperature is obtained at a reproduction beam irradiation portion of the optical disk.
In the above methods and apparatuses, the intensity of the reproduction beam may be changed stepwise from the inner side to the outer side of the optical disk, or it may be linearly, curvilinearly, or polygonally changed in accordance with the linear velocity on the basis of the information recorded on the disk.
The intensity of the reproduction beam may be changed by changing the light intensity of the reproduction light source itself, or inserting a filter between the reproduction light source and the optical disk.
Furthermore, since the reproducing apparatus can also be used as a recording apparatus by changing the intensity of the reproduction beam, it may also serve as a recording apparatus.
Although the present invention will be described in detail below with reference to its preferred embodiments, the present invention is not limited to these specific embodiments.